Solar stills for converting brackish water to fresh water by evaporating seawater to condensate that is free of salt and other contaminates are well known. However, such apparatus and methods incorporating the evaporation and condensation principles have not been entirely satisfactory in regard to the cost per gallon of fresh water. This has been particularly so with regard to systems using solar energy. Such systems generally use relatively expensive apparatus having relatively low efficiencies and producing relatively small amounts of fresh water.
A United States patent of Gerber, U.S. Pat. No. 3,257,291 represents one attempt to overcome the aforementioned problems. As disclosed therein, a desalination process and system utilize solar energy as a source of heat for effecting evaporation of the seawater and cool seawater or another natural heat sink for condensing the vapor formed in the evaporation process. As alleged, the system requires only minor amounts of power for pumping so that the operating cost per gallon of fresh water is reduced.
Another approach to desalinating water is disclosed in a U.S. Pat. No. 4,343,683 of Diggs. The Diggs patent removes contaminates from water by flowing contaminated water across a grid and into a storage tank. The grid uses solar energy to heat the water to a pre-selected temperature. A dome shaped heat transfer structure receives water from the storage tank and a pre-heater using solar energy heats the water to a further pre-selected temperature. An evaporator receives the heated water and exposes it to a vacuum so that the temperature of the water is above the saturation temperature. The water is vaporized and contaminates such as salt are separated from the water. Contaminates are deposited on a plurality of moving belts and are moved to a solids recovery system.
A more recent approach to solar distillation to provide hot or cold water for irrigation in drinking is disclosed in a U.S. Pat. No. 6,797,124 of Ludwig. The Ludwig patent employs anthracite coal as a heat-absorbing medium. A Greenhouse type roof rest over a gutter that is isolated from a water holding container to prevent deposit formation and algae growth from reaching the gutter. Bacterial growth is inhibited by ventilation and the use of titanium-laden magnetite mixed with the anthracite particles. The gutter is also isolated from the exterior of the unit, which prevents contamination from outside sources. Further, the exterior side of the roof element resting on the gutter is fitted with a metal skirt that provides a heat sink preventing the re-evaporation of condensation flowing toward the gutter.
Notwithstanding the above, it is presently believed that there is a need and a potential market for an improved solar still according to the present invention. There should be a market for such systems because they are environmentally friendly and overcome many of the disadvantages of the prior art. Systems in accordance with the present invention also provide an improved, relatively simple and environmentally friendly saline water distillation for providing potable water for drinking and irrigation in reasonably large amounts. It is also presently believed that the unit can be produced and operated at a reasonable cost, is durable and relatively easy to install and repair. The solar still in accordance with the present invention has what is believed to be a minimal number of moving parts as for example an endless heat absorbing belt which is moved around a pair of rollers at a relatively slow speed.